The Danger Below

Out of sight shouldn’t mean out of mind for cross-bore hazards.

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It seems improbable from the surface: With all the thousands of square feet of soil, what are the odds that two 6-inch pipes would get in each others’ way?

Yet, for such a seemingly unlikely situation, the potential danger of a cross bore is severe.

The ground is getting more and more crowded with buried utilities. With everything from fiber optics, communication lines, natural gas, sewer, water, and electrical lines going into the ground, the odds of running into a problem aren’t as slim as one might think.

“In the majority of instances, you don’t have any records on private property. Your typical homeowner has no idea where his or her sewer lateral is,” says Greg Scoby, Cross Bore Safety Association board member and president of Crossbore Consultants.

“When you get on private property, all bets are off. So you have to take an approach that you know there’s a minimum of water, sewer, gas, and maybe electric and communications on every parcel, and you need to proactively identify the locations of those.”

Cross bore 101

A cross bore is “the unintended conflict between two underground utility features, typically associated with trenchless installation,” according to Scoby. The biggest danger comes with gas lines.

“It becomes an immediate issue when somebody’s cleaning the drainline with the tooling used to cut roots or debris, or anything else in those lines. The plastic surfaces that are installed (for gas lines) do not present much of a barrier for that tooling,” Scoby says. “So the tooling will go ahead and cause a rupture of the gas line. … Depending on the type cutter head, plastic pipe does not have any resistance to damage. It just cuts through it like butter.”

Ruptures in the pressurized natural gas lines from cleaning equipment can cause gas to travel through the sewer laterals and back up into structures. From there, all it takes is a spark to cause a catastrophe.

There are also potential dangers when it comes to hitting electrical lines, but beyond that, the danger is minimal. Of course, cross bores still cause damage that can delay projects and cost some serious dollars for everyone involved.

“I would avoid any intrusive cleaning method without having put a camera in the line. Anything other than water — any cutting or mechanical, anything like that — I would try to take a look at the line with a camera before you do any of that stuff. That’s for sure,” says David Guillory, vice president of business development of Compliance EnviroSystems.

Prevention and mitigation

Cross-bore safety programs entail two aspects: prospecting — any predrill inspection or locating work — and postbore video inspection. Both are essential to preventing or at least mitigating cross-bore risk.

For both pre- and postinspection, video is a necessity, but Compliance EnviroSystems uses a number of locating techniques and equipment, including submeter GPS collection devices. Scoby recommends that ideal prospecting is putting a sonde down the line in addition to video inspection.

“Essentially our process is, if you’re going to be on site … we identify all the gas infrastructure related to the area that we’re inspecting,” says Nick Spano, project manager for Compliance EnviroSystems.

Compliance EnviroSystems, a sewer cleaning and evaluation company, has several contracts specifically inspecting for and identifying cross bores. That encompasses both post-bore inspection in new infrastructure and inspection of legacy systems — systems that were put in place with trenchless methods before the danger of cross bores was fully realized and safety programs put in place.

“We locate it all, using subsurface locating tools, mark it on the ground with flags and paint, and then compare it to the sewer,” Spano says.

Beyond inspection

Another important aspect of cross-bore mitigation is GIS mapping.

“This is big data. I mean, just every inspection of a lateral is megabytes of video,” Scoby says. “There’s a lot of importance in not only getting the equipment out there and inspecting, but then housing that within a data structure that allows you to go back and find that record. You can have the best information in the world, but if you can’t put your finger on it, it’s meaningless. … You need to develop some type of GIS system for it.”

When contracted to locate cross bores, Compliance EnviroSystems puts together a full data package for their clients, combining their video files with GIS to create an all-encompassing picture.

Across the industry, you’ll hear again and again that a lack of records for existing infrastructure is a huge hurdle for sewer cleaning contractors and drain installers. Getting those utilities mapped is a constant, ongoing struggle for many municipalities.

“We are mapping exactly what’s in the ground,” Spano says. “We’re pairing that with the videos and the inspection reports, and essentially then creating a map for our client that shows the exact location of all the utilities and that there are no cross bores.”

Top of mind

Though the onus is mostly on gas utility companies to avoid or repair cross bores in the first place, much of the burden eventually falls on cleaners, for whom the concern is omnipresent.

“In general, we have a number of tools that we use to clean sewer lines. … The high-pressure water — there’s really no danger in damaging the gas pipes with just the water pressure,” Spano says. “When we use some of our more invasive tools — root cutters or tap cutters, chain cutters — we have a strict policy that we never put those tools anywhere that the camera has not been.”

Cross-bore safety is part of NASSCO’s Pipeline Assessment Certification Program, and that certification is usually required by gas companies for contractors on cross-bore projects.

“It’s an issue that is going to be around for a while. There’s a lot of risk associated with it,” Scoby says. “As awareness has increased, I think most companies’ installation practices include enhanced measures, if you want to call them that, to prospect and then to verify that you did no damage. But there was a lot of intervening years there where the awareness was not as elevated as it is now.”

For cleaning contractors in the field today, cross-bore safety is summed up succinctly by Spano: “We would always inspect a pipe before putting in something that could potentially damage a gas line.”


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